Flexible highly filled compositions

ABSTRACT

Highly filled materials are disclosed. The material is formed from a composition of at least 4% by weight of a defined polar thermoplastic polymer, a plasticizer for the polymer and at least 90% by weight of an inorganic composition, including in elemental form. The compositions have a flexural modulus of less than 100 MPa. Preferably, the material provides attenuation against energy of greater than 0.1 keV that is equivalent to at least 0.1 mm of lead. The material may be used for containers, in apparel and other end-uses for protection against e.g. x-rays and gamma rays.

RELATED PATENT APPLICATION

This is a continuation of application Ser. No. 07/590,833 filed Oct. 1,1990, now abandoned, which in turn is a continuation-in-part ofapplication Ser. No. 07/440,184 filed Nov. 22, 1989, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to flexible highly filled compositions,including highly filled compositions of polymers and elastomers, thatmay be used in a variety of end-uses, including attenuation of orprotection against sound and electromagnetic radiation and as energyconducting materials. The compositions contain at least 90% by weight offiller and are flexible, with a flexural modulus of less than 100 MPa.

2. Description of the Prior Art

Highly filled compositions are capable of being used in a wide varietyof applications, especially protection against sound and againstelectromagnetic radiation and in electrically conductive applicationse.g. shielding of apparatus. Examples include mobile flexible X-rayscreens, folding X-ray doors, flexible electrical conductors, soundinsulating materials, electromagnetic energy screens for apparel e.g.protection against x-rays and beta and gamma radiation, flexiblemagnets, electrical resistant heating mats and the like, and electricalgrounding systems. In some such end-uses, it is important that thematerial be flexible and resistant against cracking e.g. apparel orcontainers, whereas in other end-uses it is preferred that the materialbe rigid e.g. in wall panels or ceiling tiles, or semi-rigid e.g. floortiles.

A number of filled materials have been proposed for use as protectionagainst radiation. For instance, Japanese patent application No.58-053928 of K. Yamamoto, published Mar. 30, 1983 discloses an elastic(rubber) foam material, preferably polychloroprene rubber, containinglarge quantities e.g. 80-87.3% by weight, of metal constituents. The useof lead oxide is disclosed, as well as the use of material containingbarium ferrite/nickel ferrite and barium ferrite/magnesium ferrite forprotection against magnetism. The compositions also contain minoramounts (<0.5%) of rubber processing aids e.g. magnesium oxide, zincoxide and lead stearate.

Japanese patent application No. 57-141430 of K. Yamamoto, published Sep.1, 1982 discloses a leaded foam material comprising a foamed materialhaving as its base a natural or synthetic rubber, preferablypolychloroprene rubber, consisting of a mixture of rubber having amolecular weight averaging 20,000 with rubber having a molecular weightranging from 2,000 to 12,000. 300 or more parts of organic and inorganiclead compounds e.g. lead oxide in amounts of 80-87.3% by weight, areadded to 100 parts by weight of the base material. The compositionscontain minor amounts (<0.5%) of rubber processing aids e.g. magnesiumoxide, zinc oxide and lead stearate.

Canadian Patent 815 609 of J. D. McCluer et al., issued Jun. 17, 1969discloses a flexible material comprising a fabric base and a layer oflead-loaded elastomeric e.g. polychloroprene, adhering to at least onesurface of the fabric base. The lead is in the form of particles of asize smaller than 200 mesh, and constitutes at least 65% by weight ofthe total weight of the material.

Metal-polymer compositions having an elongation of less than 5% areexemplified in U.S. Pat. No. 3,491,056 of F. L. Saunders et al., issuedJan. 20, 1970.

U.S. Pat. No. 4,379,190 of T. T. Schenck, issued Apr. 5, 1983 disclosescompositions of ethylene copolymers and plasticizer that contain 40-90percent by weight of filler. The fillers exemplified are calciumcarbonate and barium sulphate. Related U.S. patents include U.S. Pat.Nos. 4,191,798, 4,263,196 and 4,434,258 all of F. G. Schumacher et al.,4,403,007 of M. C. Coughlin, 4,430,468 of F. G. Schumacher and 4,438,228of T. T. Schenck.

Japanese patent application No. 61 228 051 of Dainichi Nippon Cables,published Oct. 11, 1986 discloses compositions of ethylene/vinyl acetateand/or ethylene/ethyl acrylate copolymers that contain 5-50 parts ofantimony oxide and 5-100 parts of barium sulphate, per 100 parts ofpolymer, as a wire coating composition. Cross linking of the coated wirewith electrons is disclosed.

U.S. Pat. No. 4,563,494 discloses a polymer composition formed from0.001 to 10% of at least one lanthanide oxide or hydroxide, and organicsalts or complexes and a polymer containing e.g. acrylic or methacrylicacid or ester units, for use as a shield against neutron radiation.

U.K. Patents 1 603 654 and 1 603 655, granted Nov. 25, 1981 disclosecompositions of metallic lead in polyvinyl chloride as an x-rayabsorption material.

Japanese patent application 59 126 296 of Mitsui Petrochemical,published Jul. 20, 1984 discloses the lamination of films of e.g.ethylene/vinyl acetate/carbon monoxide terpolymers onto films of e.g.ethylene/vinyl ester copolymers containing at least 50% by weight ofmetallic lead, for use in the atomic power industry.

Japanese patent application 57 005 732 of Furukawa Electric Co.,published Jan. 12, 1982 discloses compositions of polyolefins e.g.ethylene/vinyl acetate copolymers, containing 30-300 parts, per 100parts of polymer, of an inorganic powder e.g. barium borate.

Heavy, thick sound insulation using specific low cost barium salts toreplace lead compounds is disclosed in Chinese patent application86004577 of Liu et al. The addition of 100-3000 parts by weight of ametal, metal oxide, metal salts or fillers e.g. iron oxide, ferrite,lead oxide, tin oxide, barium or lead sulphate, barium or leadcarbonate, to bituminous or bituminous/rubber compositions is disclosedin Japanese patent application 60 079 065 of Ube Industries, publishedMay 4, 1985. Sound insulating sheet formed by coating iron foil withtin/lead is disclosed in Japanese patent application 60 026 651 of RikenKK, published Feb. 9, 1985.

Compositions of 100 parts of polymers and 20-800 parts of powders ofhigh specific gravity, for use in the manufacture of pipes, aredisclosed in Japanese 62 080 031 of Dainichi Nippon Cables, publishedApr. 13, 1987. Examples of the polymers are polyethylene, polypropyleneand polyvinyl chloride and of the powder are lead, iron, litharge orclay. Japanese 60 213 997 of Toyo Soda, published Oct. 26, 1985discloses sound insulation formed from 100 parts of polyvinyl chloride,200-1000 parts of inorganic filler e.g. iron oxides, barium sulphate andlead powder, and plasticizers and thylene/butene-1 copolymers and 600parts of lead monoxide are exemplified in Japanese 57 158 258 of HitachiCable KK, published Sep. 30, 1982.

Japanese Kokai 59 126 296 of S. Madao et al., published Jul. 20, 1984relates to a laminated composition for shielding against radiation,formed from lead or lead compound in a copolymer resin laminated toplasticized polyvinyl chloride. The copolymer may contain roll releasingagents, blocking inhibiting agents and the like, and the polyvinylchloride may contain tin maleate and magnesium oxide.

Although the prior art reports compositions of fillers and polymers on aweight basis, the amount of filler on a volume basis is believed to bemore important, especially with respect to processing of thecompositions. Generally, polymers filled to 5-25% by volume retain ahigh degree of flexibility, resilience, elongation, elasticity,resistance to flex cracking and the like, whereas polymers filled to20-50% by volume, if achievable with the aid of plasticizers andsuitable combinations of polymers and fillers, tend to be rigid orsemi-rigid and brittle and frequently have low resistance to flexing orlow tensile strength. In the latter, the polymer is essentially a binderor adhesive for the filler. So-called vinyl floor tiles exemplify highlyfilled polymer compositions that are generally brittle with lowflexibility.

Radiation attenuation materials in the form of mixtures of two or moreelements or compounds thereof are disclosed in U.S. Ser. No. 07/440,494of M. J. Lilley, G. E. Mawdsley, G. P. Reh and M. J. Yaffe, filed Nov.22, 1989. Radiation protection material, especially apparel, isdisclosed in U.S. Ser. No. 07/440,495 of M. J. Lilley, J. M. MacLeod, G.E. Mawdsley, G. P. Reh and M. J. Yaffe, filed Nov. 22, 1989.

SUMMARY OF THE INVENTION

A flexible highly filled polymeric composition and material formed froma thermoplastic polymer and containing elements or inorganic compounds,that may be used as an energy absorptive or conductive material e.g. forx-rays, gamma rays, sound or electricity, have now been found.

Accordingly, the present invention provides a flexible highly filledmaterial comprising a layer formed from a melt processible compositioncomprising

(a) at least 4% by weight of a thermoplastic polymer selected fromcopolymers of ethylene with at least one of vinyl acetate, alkylacrylate, alkyl methacrylate, glycidyl methacrylate, acrylic acid,methacrylic acid and carbon monoxide, and mixtures thereof, ionomers ofsuch copolymers, and such copolymers that have been grafted with amonomer selected from the group consisting of ethylenically unsaturatedcarboxylic acids and anhydrides and other derivatives thereof;

(b) a plasticizer for such copolymers; and

(c) at least 90% by weight of a solid inorganic composition that isselected from the group consisting of

(i) at least one element selected from the group consisting of aluminum,antimony, barium, bismuth, cadmium, copper, iodine, iron, lead,magnesium, mercury, nickel, silver, tantalum, tellurium, tin, thallium,tungsten, uranium and zinc,

(ii) at least one inorganic compound of an element of (i), and (iii)mixtures of (i) and (ii);

said composition having a flexural modulus of less than 100 MPa.

In a preferred embodiment of the invention, the composition has aflexural modulus of less than 70 MPa, and especially less than 30 MPa.

In a further embodiment, the layer has a thickness such that the amountof attenuation of electromagnetic radiation having energies of greaterthan 10 keV is the equivalent of at least 0.1 mm of lead.

In another embodiment, the inorganic composition contains at least oneelement, optionally in the form of an inorganic compound, selected frombismuth, lead, mercury and uranium, and at least one element selectedfrom antimony, barium, mercury, silver, tantalum, tellurium, tin andtungsten.

In yet another embodiment, the polymer composition has an elongation ofgreater than 15%, preferably greater than 100% and especially greaterthan 300 %.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a composition or material, especiallyenergy absorption or electrical conducting material, comprising at leastone layer formed from a melt processible composition comprising at least4% by weight of a thermoplastic polymer, a plasticizer for the polymerand at least 90% by weight of a solid inorganic composition; the latteris also referred to herein as inorganic component or filler. Thecompositions have a flexural modulus of less than 100 MPa, especiallyless than 70 MPa and preferably less than 30 MPa.

The polymer used to form the layer of the material of the presentinvention is selected from copolymers of ethylene with at least one ofvinyl acetate, alkyl acrylate, alkyl methacrylate, glycidylmethacrylate, acrylic acid, methacrylic acid and carbon monoxide, andmixtures thereof. The polymer may also be an ionomer of such copolymers,especially an ionomer in which the metallic ion is sodium, zinc oraluminum. In addition, the polymer may be such a copolymer that has beengrafted with a monomer selected from the group consisting ofethylenically unsaturated carboxylic acids and anhydrides and otherderivatives thereof. Examples of such polymers include ethylene/vinylacetate copolymers, ethylene/methyl acrylate copolymers, ethylene/methylmethacrylate copolymers, ethylene/acrylic acid copolymers,ethylene/alkyl acrylate/glycidyl methacrylate copolymers,ethylene/methacrylic acid copolymers, ethylene/n-butyl acrylate/carbonmonoxide copolymers, ethylene/vinyl acetate/carbon monoxide copolymersand related polymers, and sodium and zinc ionomers of ethylene/acrylicacid and methacrylic acid. As used herein, it is understood thatcopolymers may have more than two monomers i.e. include polymerssometimes referred to as terpolymers The grafted polymers include suchcopolymers that have been grafted with maleic acid or maleic anhydride.In addition, the polymers may be cross-linked, subsequent topolymerization, with ionizing radiation or cross-linking agents in orderto modify the properties of the polymer. Many examples of such polymersare available commercially e.g. from Du Pont Canada Inc., and/or thetechniques for the fabrication and/or modification of such polymers areknown in the art. In embodiments of the invention, the thermoplasticpolymer of the composition may also include polyvinyl chloride in lowproportions.

The composition used to form the layer also contains an inorganiccomponent. The inorganic component is in the form of elements per se,including alloys, or in the form of inorganic compounds of the elements.Examples of such compounds include oxides, carbonates, sulphides,carbides and hydrides; it should be understood, however, that not allinorganic compounds may be used in the compositions used to form thelayer, because of the flexibility requirements imposed thereon, as isillustrated hereinafter. The elements, or compounds, are used in afinely divided form and are uniformly dispersed throughout thethermoplastic polymer.

The particle size distribution and particle shape are importantparameters with respect to the compositions, especially to maximize thefiller loading for a predetermined flexibility and elasticity or tomaximize flexibility and elasticity at a predetermined filler loading.For instance, fine particles when coated with polymer require aconsiderable volume in comparison to the amount of filler, and increaseflexural modulus or rigidity. Thus, in preferred embodiments of thepresent invention, the filler used in the compositions has a low levelof particles smaller than 400 mesh (38 microns). It is also preferredthat the particles of largest diameter have a particle size that is notgreater than 10% of the thickness of the layer or sheet that is to beproduced from the composition e.g. a maximum particle size of 100 mesh(150 microns) is preferred In addition, the particles are preferablyspherical particles or substantially spherical particles; such particlesare often produced on grinding friable particles of larger and moreirregular shapes. Mathematical relationships relating to the preferreddistribution of particle sizes may also be derived.

The inorganic composition consists essentially of an element in the formof at least one element selected from the group consisting of aluminum,antimony, barium, bismuth, cadmium, copper, iodine, iron, lead,magnesium, mercury, nickel, silver, tantalum, tellurium, tin, thallium,tungsten, uranium and zinc. As noted above, the element may be in theform of an inorganic compound.

In preferred embodiments, the elements are selected from aluminum,antimony, barium, bismuth, cadmium, copper, iron, lead, mercury, nickel,silver, tantalum, tellurium, tin, tungsten and uranium. In furtherembodiments, the composition contains at least two of the elements, oneof which is selected from bismuth, lead, mercury and uranium, and theother is selected from antimony, barium, cadmium, silver, tantalum,tellurium, tin and tungsten.

The composition used to form the layer comprises at least 90% by weightof the inorganic component and especially at least 91% by weight ofinorganic component.

The composition also contains a plasticizer for the copolymer of thecomposition. The plasticizer must be compatible with the copolymer, andbe of a type and used in an amount that does not result in bleeding orblooming of the plasticizer from the resultant composition. Moreover,the plasticizer must be compatible with the inorganic component added aspart of the composition. Examples of such plasticizers include aromaticprocessing oils e.g. Sunthene™ 4240 plasticizer, trioctyl trimellitate,diisononyl phthalate and dioctyl phthalate. Other examples include otherphthalate esters, phosphate esters, fatty acid esters, adipates,azelates, oleates, sebacates and sulfonamides. In preferred embodiments,the compositions contain at least 2% by weight of plasticizer, andespecially at least 3% by weight of plasticizer.

The polymer composition used to form the layer may contain antioxidants,UV and other stabilizers and pigments, as will be appreciated by thoseskilled in the art.

The compositions are flexible highly filled compositions. As usedherein, flexible is understood to mean that the compositions exhibit aflexural modulus of less than 100 MPa. In preferred embodiments, thecompositions exhibit a flexural modulus of less than 70 MPa andpreferably less than 30 MPa. Flexural modulus is measured by theprocedure of ASTM D790, using 120 mil (3.18 mm) thick samples. Theflexural modulus of the composition is important in order to provideapparel that is practical for wearing or which is capable of being usedas a material for containers.

The layer of the composition is preferably of a thickness suitable forthe absorption of energy or for electrical conductivity. In particular,the thickness is such that the amount of attenuation of electromagneticradiation having energies of greater than 0.1 keV e.g. x-rays, is theequivalent of at least 0.1 mm of lead. In preferred embodiments, thethickness is such that the amount of attenuation is the equivalent of atleast 0.1 mm, especially 0.25 mm of lead and in particular at least 0.5mm of lead. Such equivalency is measured in the manner for determinationof lead equivalency known in the art, using x-rays having an energy of100 kV (also referred to as kVp), as described in Example I. In moregeneral terms, equivalence is determined by measuring the broad areatransmission of radiation of a sample of material for a radiation beamof known energy. The transmission is then measured in the same mannerfor a set of samples of commercially-pure lead of different knownthicknesses, and the equivalence for the test sample is obtained byinterpolation. Such equivalence only applies to the energy spectrum usedin the test measurements. For diagnostic x-ray protection, a typicalenergy spectrum is obtained when a potential of 100 kVp is applied to anx-ray tube. Transmission is defined as the ratio of the exposure(coulombs/kg-air) measured in an ionization chamber with material in thebeam to the corresponding exposure obtained without material in thebeam.

Measurement of the absorbence of x-rays is made by the method describedhereinafter in the examples.

In a further preferred embodiment, the composition has an elongation ofgreater than 15%, especially greater than 100% and in particular greaterthan 300%. Elongation is measured by the procedure of ASTM D-412.

If the material is to be used as electromagnetic energy absorptionmaterial in the form of apparel, it requires an acceptable flexibilityand drape, as well as acceptable resistance to flexural cracking. Such aterm is understood in the art of fabrics and related industries, andrelates to the ability of the material to conform to the contours of ahuman body or other shapes.

The compositions of the present invention are melt processible, asillustrated by melt index data given in examples hereinafter. Thecompositions may be obtained by feeding the ingredients to meltcompounding or similar equipment, the actual equipment depending in parton the actual composition to be prepared and the melt processingcharacteristics of that composition. Examples of compounding equipmentinclude two-roll mills, Banbury mixers, Farrell™ continuous mixers,Buss™ co-kneaders, Gelimat™ high intensity mixers and the like.Compositions of high content of inorganic component and/or containinggrafted polymers may be more difficult to process so as to obtainuniform compositions, and may require the use of high intensity mixersor the like. For instance, compositions of the invention may becompounded using a Banbury twin rotor internal mixer by addition of allof the ingredients into the mixer. It may, however, be preferable toprepare concentrates of plasticizer and/or the elements or compounds inpolymer, and then compound the combinations of the concentrates in ahigh shear mixer; such use of concentrates may be less hazardous tooperators of the equipment. The composition may be formed into sheet byextrusion, calendering, compression moulding or the like, a preferredmethod being by calendering.

Layer(s) of fabric may be added to the composition simultaneously withthe formation of the layer of the composition or preferably in aseparate step e.g. using a lamination technique; lamination may beachieved using adhesives or utilizing adhesive properties of the polymerused in forming the composition.

The present invention may be used in the form of apparel to protect thewearer from radiation, especially x-ray radiation, or shields forapparatus that produces radiation. The apparel may be in the form offull garments or in the form of vests or the like to protect portions ofthe human body. Alternately, the layers of the present invention may beused as containers or shields for radiation emitting products.

Although the present invention has been described with particularreference to layers of radiation protection material in the form ofapparel or containers and shields for radiation-emitting materials, itis to be understood that the layers may also be in the form of coatingson or around an object. The attenuation material of the invention mayalso be used in a variety of other end-uses.

The present invention is illustrated by the following examples; unlessnoted to the contrary, all particles were 100-,200+ mesh. As used in theexamples, exposure rate was measured using a calibrated ionizationchamber at a position 100 cm from a tungsten target x-ray tubecollimated to provide a beam measuring 8 cm×8 cm. The tube was poweredby a constant-potential x-ray generator providing 100 kV at 10 mA with aresultant half-value layer (HVL) of 5.0 mm aluminum. Variation in outputwas less than 0.5%/hour. Samples of the compositions and of lead ofknown thickness were placed in the beam, 15 cm above the ionizationchamber to determine the relative transmissions, and the leadequivalence for the composition was obtained by interpolation.

EXAMPLE I

A composition of metallic lead (92% by weight) in a blend ofethylene/vinyl acetate copolymers containing Sunthene 4240 aromaticprocessing oil was prepared using the Brabender melt processingapparatus. The metallic lead comprised 49% by volume of the composition;the lead had a particle size distribution such that 1-2% (by weight)would pass through a 100 mesh screen, an additional 24-28% would passthrough a 200 mesh screen, an additional 25-30% would pass through a 325mesh screen and the remainder was retained on the latter screen. Thecomposition, of density 6.05 g/cm³, was formed into highly flexiblesheet having a thickness of 46 microns (18 mil).

It was found that for absorption equivalent to 0.5 mm of lead, thecomposition weighed 6.1 kg/m², and that the weight saving compared withlead-vinyl was 16%, with the same absorption.

The sheet of this example could be used for attenuation of x-rays andgamma rays, as well as for absorption of sound.

EXAMPLE II

A composition of copper powder (90.3% by weight) in a blend ofethylene/vinyl acetate copolymers containing Sunthene 4240 aromaticprocessing oil was prepared using the Brabender melt processingapparatus. The metallic copper comprised 50% by volume of thecomposition; the copper had a particle size distribution such that 27%(by weight) would pass through a 150 mesh screen, an additional 49%would pass through a 200 mesh screen, an additional 22% would passthrough a 325 mesh screen and the remainder was retained on the latterscreen. The composition, of density 4.93 g/cm³, was formed into highlyflexible electrically conductive sheet having a thickness of 56 microns(22 mil).

EXAMPLE III

A composition of metallic lead (32.2% by weight), metallic tin (27.6% byweight) and metallic tungsten (32.3% by weight) was prepared in anethylene/vinyl acetate copolymer (7.9% by weight) using the Brabendermelt processing apparatus; thus, the composition contained 92.1% byweight of inorganic components. The polymer composition obtained had adensity of 6.03 g/cm³.

Computer analysis indicated that the sample would provide a sampleweight saving compared to lead/vinyl of 38%, for the same x-rayattenuation/absorption, based on thicknesses equivalent to 0.5 mm oflead.

EXAMPLE IV

A composition of lead sulphide (90% by weight) in a blend ofethylene/vinyl acetate copolymers (6% by weight) containing Sunthene4240 aromatic processing oil (4% by weight) was prepared; the leadsulphide was a dry blend of lead sulphide (86%) and fine silicaceoussand (14%). The composition had a density of 4.44 g/cm³ and a fillercontent of 90% by weight and 55% by volume. Sheet formed from thecomposition was flexible, tough and resilient.

As a comparison, a composition was formed from lead sulphide (85.5% byweight) in polyvinyl chloride (8.5% by weight) and dioctyl phthalateplasticizer (6% by weight). The composition had a density of 4.27 g/cm³and a filler content of 85.5% by weight and 50% by volume. Sheet formedfrom this composition was brittle with no significant tensile strengthor flexibility.

This example shows that polyvinyl chloride would have to be used atfiller loadings that are lower than those used with the ethylene/vinylacetate copolymer, and with a corresponding increase in overall weight,volume and thickness in order to achieve the same amount of x-rayattenuation.

EXAMPLE V

A series of compositions were prepared with the same polymer andplasticizer compositions but with differing 200 mesh metallic lead, 325mesh metallic lead and barium sulphate; the latter filler is a fillerused in the aforementioned compositions of Schumacher and others.

The polymer was Elvax® 265 ethylene/vinyl acetate copolymer and theplasticizer was Sunthene 4240 aromatic processing oil. A small amount ofKemamide™ "U" slip agent and Nordel 2744 ethylene/propylene elastomer,to improve flex-cracking resistance, were added at levels of less than0.5% by weight.

Physical property measurements were made on the compositions, using thefollowing procedures:

Melt Index--procedure of ASTM D-1238 (condition E)

Tensile Strength--procedure of ASTM D-412

Elongation--procedure of ASTM D-412

Flexural Modulus--procedure of ASTM D-790

Further details and the results obtained were as follows:

                  TABLE I                                                         ______________________________________                                        Run No.    1        2       3       4    5                                    ______________________________________                                        Composition                                                                   Polymer (wt %)                                                                Elvax 265  5.37     4.84    4.84    4.30 4.84                                 Nordel 2744                                                                              0.27     0.24    0.24    0.22 0.24                                 Plasticizer                                                                   Kemamide U 0.54     0.49    0.49    0.44 0.49                                 Sunthene 4240                                                                            3.81     3.43    3.43    3.05 3.43                                 Filler                                                                        Lead (#200)                                                                              90.0     --      91.0    92.0 --                                   Lead (#325)                                                                              --       91.0    --      --                                        BaSO.sub.4 --       --      --      --   91.0                                 Properties                                                                    Density    5.35     5.56    5.66    6.03 3.11                                 Melt Index 48.1     38.3    --      27.2 NF                                   Tensile str.                                                                             2.4      2.6     2.4     2.0  0.37                                 Elongation 505      760     515     19   5                                    Flex. mod. 32       2       39      44   NM                                   ______________________________________                                         Note: NF = no flow;                                                           NM = not measurable, sample was brittle and cracked;                          Density is reported in g/cm.sup.3 ;                                           Melt index is reported in dg/min;                                             Tensile strength is reported in MPa;                                          Elongation is reported as a percentage;                                       Flexural modulus is reported in MPa and was measured on samples having a      thickness of 120 mil (3.18 mm)                                           

The results show that a composition prepared with barium sulphate as thefiller, in a polymer composition that contained a plasticizer, wasbrittle with an elongation of only 5%; the melt index test indicatesthat the composition was not melt processible. Thus, the compositionswith barium sulphate as filler are outside the scope of the presentinvention.

In contrast, the other compositions, using the same polymer andplasticizer at the same % composition by weight, were flexible and hadgood stretch, as indicated by the flexural modulus of 32-52 MPa andelongation of up to 760%. The compositions were melt processible, asindicated by the high values of melt index that were obtained.

Thus, the nature of the filler is critical to the properties of thecomposition that is obtained.

EXAMPLE VI

The procedure of Run 3 of Example V was repeated, except that the leadpowder was oiled, to reduce dust particulates during processing, priorto blending with the polymer; the oil used was an aromatic hydrocarbonoil. The compositions were prepared by compounding in a Brabenderapparatus, and then compression moulding.

It was found that the composition obtained had an elongation of 24%,compared with 515% for the composition of Run 3. In addition, inmeasurement of tensile properties, the composition did not exhibit ayield point and had an ultimate tensile strength of 2.92 MPa, whereasthe composition of Run 3 had a yield point at an elongation of 48% and atensile strength of 2.08 MPa.

This Example shows the substantial effect of oiling the filler prior tocompounding with the polymer composition. While this Example illustratesthe invention, comparison with the results of Run 3 shows that themethod of processing of the composition may have an effect on theproperties of the sheet (layer) obtained.

EXAMPLE VII

A series of compositions were prepared using pre-oiled filler viz. 200mesh lead powder, but using a calendaring process to prepare sheetrather than a compression moulding process.

Further experimental details and the results obtained are given in TableII.

                  TABLE II                                                        ______________________________________                                        Run No.    7        8       9       10   11                                   ______________________________________                                        Composition                                                                   Polymer (wt %)                                                                Elvax 265  6.02     5.37    4.84    4.30 3.87                                 Nordel 2744                                                                              0.30     0.27    0.24    0.22 0.20                                 Plasticizer                                                                   Sunthene 4240                                                                            4.27     3.81    3.43    3.05 2.74                                 Kemamide U 0.61     0.54    0.49    0.44 0.39                                 Filler     88.8     90.     91.0    92.0 92.8                                 Properties                                                                    Density    4.70     4.89    5.56    5.93 6.23                                 Melt Index 28.1     20.2    18.0    12.9 11.8                                 Flex. Mod. 55.3     50.9    69.3    91.5 108                                  Tensile str.                                                                  MD         4.51     5.76    5.90    6.18 6.94                                 TD         2.57     2.57    2.08    2.22 2.92                                 Elongation                                                                    MD         140      65      60      60   40                                   TD         400      160     90      65   60                                   ______________________________________                                         Note: Density is reported in g/cm.sup.3 ;                                     Melt index is reported in dg/min;                                             Tensile strength is reported in MPa;                                          Elongation is reported as a percentage;                                       Flexural modulus is reported in MPa, and was measured on samples having a     thickness of 120 mil (3.18mm)                                                 MD = machine direction, TD = transverse direction                             Run 7 is a comparative run                                               

This example shows that flexible sheet may be obtained using acalendaring process and a pre-oiled filler.

The compositions have high densities, up to 6.2 g/cm³, and are excellentabsorbers of radiation. The sheets of Runs 8-11 weigh only 7-11% morethan sheet lead, which is commonly used for x-ray or sound absorption),but are flexible, easily heat-formed, weldable and with good flex crackresistance. There is a weight saving of about 14% over lead-vinyl, whichtypically has about 80% lead content.

Comparison of the data in Table II with that in Run 5 shows that thecompositions of the invention show a 5-19 fold increase in tensilestrength, as well as good elongation and flexibility.

We claim:
 1. A flexible highly filled radiation shielding sheetconsisting essentially of:(a) at least 4% by weight of a thermoplasticpolymer selected from copolymers of ethylene including vinyl acetate andblends of such copolymers with ethylene/propylene elastomers; (b) aplasticizer for such copolymers; and (c) at least 90% by weight of asolid inorganic element or compound selected from the group consistingof copper, lead, tin, tungsten, and lead sulphide and mixtures thereof;said sheet having a flexural modulus of less than 100 MPa and anelongation of at least 15%.
 2. The highly filled sheet of claim 1 inwhich the sheet has a flexural modulus of less than 70 MPa.
 3. Thehighly filled sheet of claim 6 in which the sheet has a flexural modulusof less than 35 MPa.
 4. The highly filled sheet of claim 1 in which thesheet has a thickness such that the amount of attenuation ofelectromagnetic radiation having energies of greater than 10 keV is theequivalent of at least 0.1 mm of lead.
 5. The highly filled sheet ofclaim 1 in which the sheet has an elongation of at least 100%.
 6. Thehighly filled sheet of claim 1 in which the sheet has an elongation ofat least 300%.
 7. The highly filled sheet of claim 1 in which theinorganic element or compounds are in the form of particles having asize in the range of 38-150 microns.
 8. The highly filled sheet of claim1 in which the sheet has a thickness such that the amount of attenuationof electromagnetic radiation having energies of greater than 10 keV isthe equivalent of at least 0.1 mm of lead.